The captain of a US navy aircraft carrier facing a growing outbreak of the novel coronavirus is asking for permission to isolate the bulk of his roughly 5,000 crew members onshore, which would take the warship out of duty in an effort to save lives.

In a memo to navy leaders, the captain of the USS Theodore Roosevelt said the spread of the COVID-19 disease is continuing and accelerating and that removing all but 10 percent of the crew is a "necessary risk" to stop the spread of the virus. The ship is docked in Guam.

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Navy leaders were on Tuesday scrambling to determine how to best respond to the extraordinary request as dozens of crew members tested positive.

"We are not at war. Sailors do not need to die. If we do not act now, we are failing to properly take care of our most trusted asset - our sailors," said Captain Brett Crozier in a memo obtained by The Associated Press news agency.

A navy official said Crozier alerted commanders on Sunday evening of the continuing challenges in isolating the virus. The official, who spoke on condition of anonymity to discuss internal deliberations, said Crozier wants more isolated housing for the crew and that navy leadership is reviewing options to ensure the health and safety of the crew.

Trump has consistently touted his support for the US military [Al Drago/Reuters]

US Pacific Fleet commander Admiral John Aquilino told reporters on Tuesday that the navy is working to get as many sailors as possible onshore, while still maintaining a core crew to monitor the nuclear reactors and keep the ship running.

He said the pace may not be as fast as the commander would like, but it will be done on a rotation, with sailors staying onshore in isolation for 14 days, then returning to the ship virus-free so that others can go ashore.

Asked about efforts to isolate sailors onshore, he said the navy is doing what it can with facilities that are available. Officials are working with the government of Guam to try to get hotel rooms that will allow for greater isolation, Aquilino said.

Aquilino would not discuss exact numbers or timelines, but agreed with navy Secretary Thomas Modly's assertion that about 1,000 sailors have been taken off the ship so far. He added that no sailors are currently hospitalised.

For most people, the new coronavirus causes mild or moderate symptoms, such as fever and cough, that clear up in two to three weeks. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia, and death.

Fundamental shift

In Asia, a carrier presence is central to what the Pentagon has identified as a fundamental shift from fighting certain conflicts in the Middle East to a return to "great power competition". That means, principally, a bigger focus on China, including its militarisation of disputed areas of the South China Sea.

The outbreak on the carrier may be the navy's most dramatic, but it tracks an accelerating upward trend across the military. The Pentagon said the number of cases in the military had reached 673 on Tuesday morning, a jump of 104 from the day before and up from 174 a week ago.

Since March 20, the total has surged tenfold, even as the Pentagon has taken many steps to try to limit the spread, including halting nearly all movement of troops overseas.

The carrier, like other navy ships, is vulnerable to infectious disease spread given its close quarters. The massive ship is more than 1,000 feet (305 metres) long; sailors are spread out across a labyrinth of decks linked by steep ladder-like stairs and narrow corridors. Enlisted sailors and officers have separate living quarters, but they routinely grab their food from crowded buffet lines and eat at tables joined end-to-end.

Listing many of those problems, Crozier's memo, which was first reported by the San Francisco Chronicle, warns that the close quarters means that thousands of sailors now require quarantine. He said sailors have been moving off the ship into shore-based quarters, but much of that is also not adequate. He said much of the off-ship locations available so far are group quarantine sites, and already two sailors housed in an auditorium have tested positive for the virus.

To stop the spread of the virus and prevent death, Crozier said they must take a methodical approach, move the majority of the sailors off the ship, isolate them and completely clean it. He said about 10 percent of the crew would have to stay on board to secure the vessel, run critical systems and sanitise everything. Aquilino declined to confirm that estimate but said he is working with commanders to get people quarantined and tested as quickly as possible.

Necessary risk

While removing that many may seem like an extraordinary measure, Crozier said it is a necessary risk.

"It will enable the carrier and air wing to get back under way as quickly as possible while ensuring the health and safety of our sailors," Crozier said, adding that finding appropriate isolation for the crew "will require a political solution, but it is the right thing to do".

Modly told CNN that efforts were under way to help the ship while ensuring that the navy and the US military continue to protect the country.

"This is a unique circumstance," he said. "And we're working through it and trying to maintain that proper balance to ensure that our friends and allies, and most importantly our foes and adversaries out there, understand that we are not standing down the watch.